Prevention of spontaneous preterm delivery – an update on where we are today

Spontaneous preterm birth (delivery before 37 completed weeks) is the single most important cause of perinatal morbidity and mortality. The rate is increasing world-wide with a great disparity between low, middle and high income countries. It has been estimated that the cost of neonatal care for preterm babies is more than 4 times that of a term neonate admitted into the neonatal care. Furthermore, there are high costs associated with long-term morbidity in those who survive the neonatal period. Interventions to stop delivery once preterm labor starts are largely ineffective hence the best approach to reducing the rate and consequences is prevention. This is either primary (reducing or minimizing factors associated with preterm birth prior to and during pregnancy) or secondary - identification and amelioration (if possible) of factors in pregnancy that are associated with preterm labor. In the first category are optimizing maternal weight, promoting healthy nutrition, smoking cessation, birth spacing, avoidance of adolescent pregnancies and screening for and controlling various medical disorders as well as infections prior to pregnancy. Strategies in pregnancy, include early booking for prenatal care, screening and managing medical disorders and their complications, and identifying predisposing factors to preterm labor such as shortening of the cervix and timely instituting progesterone prophylaxis or cervical cerclage where appropriate. The use of biomarkers such as oncofetal fibronectin, placental alpha-macroglobulin-1 and IGFBP-1 where cervical screening is not available or to diagnosis PPROM would identify those that require close monitoring and allow the institution of antibiotics especially where infection is considered a predisposing factor. Irrespective of the approach to prevention, timing the administration of corticosteroids and where necessary tocolysis and magnesium sulfate are associated with an improved outcome. The role of genetics, infections and probiotics and how these emerging dimensions help in the diagnosis of preterm birth and consequently prevention are exciting and hopefully may identify sub-populations for targeted strategies.

Role of Transcription Factors in the Management of Preterm Birth: Impact on Future Treatment Strategies

Preterm birth is defined as the birth of a neonate before 37 weeks of gestation and is considered as a leading cause of the under five deaths of neonates. Neonates born preterm are known to have higher perinatal mortality and morbidity with associated risks of low birth weight, respiratory distress syndrome, gastrointestinal, immunologic, central nervous system, hearing, and vision problems, cerebral palsy, and delayed development. India leads the list of countries with the greatest number of preterm births. The studies focusing on the molecular mechanisms related to the etiology of preterm birth have described the role of different transcription factors. With respect to this, transcription factors like peroxisome proliferator activated receptors (PPAR), nuclear factor kappa β (NF-kβ), nuclear erythroid 2-related factor 2 (Nrf2), and progesterone receptor (PR) are known to be associated with preterm labor. All these transcription factors are linked together with a common cascade involving inflammatory processes. Thus, the current review describes the possible cross-talk between these transcription factors and their therapeutic potential to prevent or manage preterm labor.

Progesterone receptor genetic variants in pregnant women and fetuses as possible predictors of spontaneous premature birth: A preliminary case-control study

AIM

To evaluate the roles of four selected genetic variations in fetal and maternal progesterone receptor gene (PGR) and to identify women who may have higher or lower odds for spontaneous premature birth compared to the general population.

METHODS

A preliminary case-control study with two groups of pregnant women (with term and premature delivery, 218 in total) and two groups of newborns (term and preterm, 218 in total) was performed. Four single nucleotide polymorphisms (SNPs) of the progesterone receptor gene (rs1042838, rs1042839, rs10895068, and rs1942836) were genotyped.

RESULTS

There was statistically significant difference between cases and controls in the distribution of newborns' allele frequency of minor C allele of the PGR SNP rs1942836 (p = 0.03, Fishers' exact test) in favor of premature birth. A statistically significant difference between the frequency of the mothers' minor T allele of rs1042838 (p = 0.005; chi-squared test) and the mothers' minor T allele of rs1042839 (p = 0.005; chi-squared test) in favor of extremely premature birth has been found. There was a statistically significant difference between the frequency of the newborns' minor C allele of rs1942836 (p = 0.03; chi-squared test) and newborns' heterozygotes CT genotype of rs1942836 (p = 0.03; Fishers' exact test) when comparing the group of term births and the group of early premature birth.

CONCLUSION

Our study suggests that patients with selected genetic variants of the progesterone receptor gene could have greater odds for premature birth compared to term birth. Replication studies with a larger population and different ethnicity are needed in order to confirm these findings.

A systematic review and meta-analysis of randomized controlled trials comparing 17-alpha-hydroxyprogesterone caproate versus placebo for the prevention of recurrent preterm birth

BACKGROUND

Preterm birth causes an increased risk for perinatal morbidity and mortality.

OBJECTIVE

To determine whether mid-trimester 17-alpha-hydroxyprogesterone caproate (17-OHPC) reduces the risk of recurrent preterm birth and adverse perinatal outcomes.

SEARCH STRATEGY

Systematic search to identify relevant studies published in different languages, registered after 2000, using appropriate MeSH terms.

SELECTION CRITERIA

Inclusion criteria were women between 16 and 26⁺⁶  weeks of pregnancy with history of preterm delivery in any pregnancy randomized to either 17-OHPC or placebo/no treatment.

DATA COLLECTION AND ANALYSIS

The number of preterm births and adverse outcomes in the 17-OHPC and placebo arms over the total number of patients in each randomized group were used to calculate the risk ratio (RR) by random-effects models using the Mantel-Haenszel method. Between-study heterogeneity was assessed using tau² , χ² (Cochrane Q), and I² statistics.

MAIN RESULTS

Four studies were included. There was a 29% (RR 0.71; 95% CI, 0.53-0.96; P=0.001), 26% (RR 0.74; 95% CI, 0.58-0.96; P=0.021), and 40% (RR 0.60; 95% CI, 0.42-0.85; P=0.004) reduction in recurrent preterm birth at <37, <35, and <32 weeks, respectively, in the 17-OHPC group compared with placebo. The reduction in neonatal death was 68% (RR 0.32; 95% CI, 0.15-0.66; P=0.002).

CONCLUSIONS

17-OHPC could reduce the risk of recurrent preterm birth at <37, <35, and <28 weeks and neonatal death.

PROSPERO

CDR42017082190.

The association among cytochrome P450 3A, progesterone receptor polymorphisms, plasma 17-alpha hydroxyprogesterone caproate concentrations, and spontaneous preterm birth

BACKGROUND

Infants born <37 weeks' gestation are of public health concern since complications associated with preterm birth are the leading cause of mortality in children <5 years of age and a major cause of morbidity and lifelong disability. The administration of 17-alpha hydroxyprogesterone caproate reduces preterm birth by 33% in women with history of spontaneous preterm birth. We demonstrated previously that plasma concentrations of 17-alpha hydroxyprogesterone caproate vary widely among pregnant women and that women with 17-alpha hydroxyprogesterone caproate plasma concentrations in the lowest quartile had spontaneous preterm birth rates of 40% vs rates of 25% in those women with higher concentrations. Thus, plasma concentrations are an important factor in determining drug efficacy but the reason 17-alpha hydroxyprogesterone caproate plasma concentrations vary so much is unclear. Predominantly, 17-alpha hydroxyprogesterone caproate is metabolized by CYP3A4 and CYP3A5 enzymes.

OBJECTIVE

We sought to: (1) determine the relation between 17-alpha hydroxyprogesterone caproate plasma concentrations and single nucleotide polymorphisms in CYP3A4 and CYP3A5; (2) test the association between progesterone receptor single nucleotide polymorphisms and spontaneous preterm birth; and (3) test whether the association between plasma concentrations of 17-alpha hydroxyprogesterone caproate and spontaneous preterm birth varied by progesterone receptor single nucleotide polymorphisms.

STUDY DESIGN

In this secondary analysis, we evaluated genetic polymorphism in 268 pregnant women treated with 17-alpha hydroxyprogesterone caproate, who participated in a placebo-controlled trial to evaluate the benefit of omega-3 supplementation in women with history of spontaneous preterm birth. Trough plasma concentrations of 17-alpha hydroxyprogesterone caproate were measured between 25-28 weeks of gestation after a minimum of 5 injections of 17-alpha hydroxyprogesterone caproate. We extracted DNA from maternal blood samples and genotyped the samples using TaqMan (Applied Biosystems, Foster City, CA) single nucleotide polymorphism genotyping assays for the following single nucleotide polymorphisms: CYP3A4*1B, CYP3A4*1G, CYP3A4*22, and CYP3A5*3; and rs578029, rs471767, rs666553, rs503362, and rs500760 for progesteronereceptor. We adjusted for prepregnancy body mass index, race, and treatment group in a multivariable analysis. Differences in the plasma concentrations of 17-alpha hydroxyprogesterone caproate by genotype were evaluated for each CYP single nucleotide polymorphism using general linear models. The association between progesterone receptor single nucleotide polymorphisms and frequency of spontaneous preterm birth was tested using logistic regression. A logistic model also tested interaction between 17-alpha hydroxyprogesterone caproate concentrations with each progesterone receptor single nucleotide polymorphism for the outcome of spontaneous preterm birth.

RESULTS

The association between CYP single nucleotide polymorphisms *22, *1G, *1B, and *3 and trough plasma concentrations of 17-alpha hydroxyprogesterone caproate was not statistically significant (P = .68, .44, .08, and .44, respectively). In an adjusted logistic regression model, progesterone receptor single nucleotide polymorphisms rs578029, rs471767, rs666553, rs503362, and rs500760 were not associated with the frequency of spontaneous preterm birth (P = .29, .10, .76, .09, and .43, respectively). Low trough plasma concentrations of 17-alpha hydroxyprogesterone caproate were statistically associated with a higher frequency of spontaneous preterm birth (odds ratio, 0.78; 95% confidence ratio, 0.61-0.99; P = .04 for trend across quartiles), however no significant interaction with the progesterone receptor single nucleotide polymorphisms rs578029, rs471767, rs666553, rs503362, and rs500760 was observed (P = .13, .08, .10, .08, and .13, respectively).

CONCLUSION

The frequency of recurrent spontaneous preterm birth appears to be associated with trough 17-alpha hydroxyprogesterone caproate plasma concentrations. However, the wide variation in trough 17-alpha hydroxyprogesterone caproate plasma concentrations is not attributable to polymorphisms in CYP3A4 and CYP3A5 genes. Progesterone receptor polymorphisms do not predict efficacy of 17-alpha hydroxyprogesterone caproate. The limitations of this secondary analysis include that we had a relative small sample size (n = 268) and race was self-reported by the patients.

Spontaneous preterm birth and single nucleotide gene polymorphisms: a recent update

Background

Preterm birth (PTB), birth at <37 weeks of gestation, is a significant global public health problem. World-wide, about 15 million babies are born preterm each year resulting in more than a million deaths of children. Preterm neonates are more prone to problems and need intensive care hospitalization. Health issues may persist through early adulthood and even be carried on to the next generation. Majority (70 %) of PTBs are spontaneous with about a half without any apparent cause and the other half associated with a number of risk factors. Genetic factors are one of the significant risks for PTB. The focus of this review is on single nucleotide gene polymorphisms (SNPs) that are reported to be associated with PTB.

Results

A comprehensive evaluation of studies on SNPs known to confer potential risk of PTB was done by performing a targeted PubMed search for the years 2007–2015 and systematically reviewing all relevant studies. Evaluation of 92 studies identified 119 candidate genes with SNPs that had potential association with PTB. The genes were associated with functions of a wide spectrum of tissue and cell types such as endocrine, tissue remodeling, vascular, metabolic, and immune and inflammatory systems.

Conclusions

A number of potential functional candidate gene variants have been reported that predispose women for PTB. Understanding the complex genomic landscape of PTB needs high-throughput genome sequencing methods such as whole-exome sequencing and whole-genome sequencing approaches that will significantly enhance the understanding of PTB. Identification of high risk women, avoidance of possible risk factors, and provision of personalized health care are important to manage PTB.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3089-0) contains supplementary material, which is available to authorized users.

What we have learned about the role of 17-alpha-hydroxyprogesterone caproate in the prevention of preterm birth

Despite major advances in neonatal care, the burden of preterm birth remains high. This is not unexpected since strategies to identify and treat risk factors in early pregnancy have not been very effective in reducing the preterm birth rate. Initial studies suggested a potential benefit for 17-alpha-hydroxyprogesterone caproate (17-OHPC) in decreasing the risk of recurrent preterm birth women with a singleton gestation. However, the use of 17-OHPC has not conferred benefit for other categories of women at high risk for preterm delivery (twins, triplets, and short cervical length). The increasing body of evidence suggests that preterm birth is a complex condition with variable mechanisms of disease and significant individual heterogeneity. This review will examine the plausibility of 17-OHPC in preventing preterm birth and the investigation of its clinical efficacy. We will also highlight factors to explain variations in clinical trial outcomes and outline the trajectory needed for future investigations.

PROGESTERONE RECEPTOR GENE POLYMORPHISMS AS GENETIC RISK FACTOR OF THREATENED ABORTION

Determination of the progesterone receptor gene polymor- phisms rs590688 C/G and rs500760 A/G was provided using PCR method. To investigate the genetical precursors of threatened abortion the next groups were included: 67 patients with threatened abortion and 93 healthy persons. These allelic variants have the significantly different at rs590688 study: C/C - 23,9%, C/G - 44,8%, GIG - 31,3%, and C/C - 27,2%, C/G - 58,7%, GIG - 14,1% in the control group (P<0,05 by x2-test). The allelic variants of the rs500760 polymorphism did not differ statistically in the study group A/A 53,7%, A/G - 40,3%, GIG - 6% in the control group A/A- 52,2%, A/G - 44,6%, GIG - 3,3% (P>0,05 by x2-test). Distribution of minor homozygote GIG polymorphism rs590688 progesterone receptor gene in patients with threatened abortion in our study almost in 10 times higher in comparing with women of Taiwanese Han population, who had idiopathic recurrent pregnancy loss. The obtained data indicate significant ethnic differences in PGR and show polymorphism rs590688 clinical significance.

[SINGLE NUCLEOTIDE POLYMORPHISMS IN HUMAN PROGESTERONE RECEPTOR GENE AND ITS VALUE IN MISCARRIAGE OR PRETERM DELIVERY]

This article presents the current understanding of progesterone and its role in female reproductive function, described the structure and functionality of the progesterone receptor. The attention is focused on the meaning of the terms miscarriage and preterm delivery. Was described the today known causes of the miscarriage and preterm delivery, shown the value of single nucleotide polymorphisms of the progesterone receptor in miscarriage and preterm delivery by the analysis of publications in recent years in order to find connections between different polymorphisms of the progesterone receptor gene and a spontaneous abortion, premature labor, recurrent miscarriage and its impact on progesterone therapy.

Genomics of preterm birth

The molecular mechanisms controlling human birth timing at term, or resulting in preterm birth, have been the focus of considerable investigation, but limited insights have been gained over the past 50 years. In part, these processes have remained elusive because of divergence in reproductive strategies and physiology shown by model organisms, making extrapolation to humans uncertain. Here, we summarize the evolution of progesterone signaling and variation in pregnancy maintenance and termination. We use this comparative physiology to support the hypothesis that selective pressure on genomic loci involved in the timing of parturition have shaped human birth timing, and that these loci can be identified with comparative genomic strategies. Previous limitations imposed by divergence of mechanisms provide an important new opportunity to elucidate fundamental pathways of parturition control through increasing availability of sequenced genomes and associated reproductive physiology characteristics across diverse organisms.

Prevention of preterm delivery with 17-hydroxyprogesterone caproate: pharmacologic considerations

Despite advances in neonatal care, the burden of preterm birth remains high. Preterm birth is a multifactorial problem, and strategies to identify and treat medical risk factors in early pregnancy have not been effective in reducing preterm birth rates. In a sentinel clinical trial, prophylactic therapy with 17-hydoxyprogesterone caproate (17-OHPC) reduced the risk of recurrent, spontaneous preterm birth in 34% of women. As a result, clinical practice changed and extensive research on 17-OHPC followed. The increasing body of evidence demonstrated a variable efficacy of the drug. This review will examine the plausibility, pharmacology, clinical efficacy, and safety of 17-OHPC when used in the setting of preterm birth prevention. We will also discuss pharmacokinetic and pharmacodynamics data to highlight drug metabolism and mechanism of action, which will help clarify the variability in clinical outcomes and efficacy.

Imitating a stress response: a new hypothesis about the innate immune system's role in pregnancy

Recent research challenges long-held hypotheses about mechanisms through which pregnancy induces maternal immune suppression or tolerance of the embryo/fetus. It is now understood that normal pregnancy engages the immune system and that the immune milieu changes with advancing gestation. We suggest that pregnancy mimics the innate immune system's response to stress, causing a sterile inflammatory response that is necessary for successful reproduction. The relationship between external stressors and immunomodulation in pregnancy has been acknowledged, but the specific mechanisms are still being explicated. Implantation and the first trimester are times of immune activation and intensive inflammation in the uterine environment. A period of immune quiescence during the second trimester allows for the growth and development of the maturing fetus. Labor is also an inflammatory event. The length of gestation and timing of parturition can be influenced by environmental stressors. These stressors affect pregnancy through neuroendocrine interaction with the immune system, specifically through the hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-ovarian axis. Trophoblastic cells that constitute the maternal-fetal interface appear to harness the maternal immune system to promote and maximize the reproductive success of the mother and fetus. Pregnancy is a time of upregulated innate immune responses and decreased adaptive, cell-mediated responses. The inflammatory processes of pregnancy resemble an immune response to brief naturalistic stressors: there is a shift from T helper (Th) 1 to T helper (Th) 2 dominant adaptive immunity with a concomitant shift in cytokine production, decreased proliferation of T cells, and decreased cytotoxicity of natural killer (NK) cells. Inclusion of both murine and human studies, allows an exploration of insights into how trophoblasts influence the activity of the maternal innate immune system during gestation.

A Genome-Wide Association Study of spontaneous preterm birth in a European population

Background: Preterm birth is defined as a birth prior to 37 completed weeks’ gestation. It affects more than 10% of all births worldwide, and is the leading cause of neonatal mortality in non-anomalous newborns. Even if the preterm newborn survives, there is an increased risk of lifelong morbidity. Despite the magnitude of this public health problem, the etiology of spontaneous preterm birth is not well understood. Previous studies suggest that genetics is an important contributing factor. We therefore employed a genome-wide association approach to explore possible fetal genetic variants that may be associated with spontaneous preterm birth.Methods: We obtained preterm birth phenotype and genotype data from the National Center for Biotechnology Information Genotypes and Phenotypes Database (study accession phs000103.v1.p1). This dataset contains participants collected by the Danish National Birth Cohort and includes 1000 preterm births and 1000 term births as controls. Whole genomes were genotyped on the Illumina Human660W-Quad_v1_A platform, which contains more than 500,000 markers. After data quality control, we performed genome-wide association studies for the 22 autosomal chromosomes.Results: No single nucleotide polymorphism reached genome-wide significance after Bonferroni correction for multiple testing.Conclusion: We found no evidence of genetic association with spontaneous preterm birth in this European population. Approaches that facilitate detection of both common and rare genetic variants, such as evaluation of high-risk pedigrees and genome sequencing, may be more successful in identifying genes associated with spontaneous preterm birth.

California Very Preterm Birth Study: design and characteristics of the population- and biospecimen bank-based nested case-control study

Very preterm birth (VPTB) is a leading cause of infant mortality, morbidity and racial disparity in the US. The underlying causes of VPTB are multiple and poorly understood. The California Very Preterm Birth Study was conducted to discover maternal and infant genetic and environmental factors associated with VPTB. This paper describes the study design, population, data and specimen collection, laboratory methods and characteristics of the study population. Using a large, population-based cohort created through record linkage of livebirths delivered from 2000 to 2007 in five counties of southern California, and existing data and banked specimens from statewide prenatal and newborn screening, 1100 VPTB cases and 796 control mother-infant pairs were selected for study (385/200 White, 385/253 Hispanic and 330/343 Black cases/controls, respectively). Medical record abstraction of cases was conducted at over 50 hospitals to identify spontaneous VPTB, improve accuracy of gestational age, obtain relevant clinical data and exclude cases that did not meet eligibility criteria. VPTB was defined as birth at <32 weeks in Whites and Hispanics and <34 weeks in Blacks. Approximately 55% of all VPTBs were spontaneous and 45% had medical indications or other exclusions. Of the spontaneous VPTBs, approximately 41% were reported to have chorioamnionitis. While the current focus of the California Very Preterm Birth Study is to assess the role of candidate genetic markers on spontaneous VPTB, its design enables the pursuit of other research opportunities to identify social, clinical and biological determinants of different types of VPTB with the ultimate aim of reducing infant mortality, morbidity and racial disparities in these health outcomes in the US and elsewhere.

Progesterone receptor polymorphisms and clinical response to 17-alpha-hydroxyprogesterone caproate

OBJECTIVE

Seventeen-alpha-hydroxyprogesterone caproate (17-OHPC) reduces recurrent preterm birth (PTB). We hypothesized that single nucleotide polymorphisms in the human progesterone receptor (PGR) affect response to 17-OHPC in the prevention of recurrent PTB.

STUDY DESIGN

We conducted secondary analysis of a study of 17-OHPC vs placebo for recurrent PTB prevention. Twenty PGR gene single nucleotide polymorphisms were studied. Multivariable logistic regression assessed for an interaction between PGR genotype and treatment status in modulating the risk of recurrent PTB.

RESULTS

A total of 380 women were included; 253 (66.6%) received 17-OHPC and 127 (33.4%) received placebo. In all, 61.1% of women were African American. Multivariable logistic regression demonstrated significant treatment-genotype interactions (either a beneficial or harmful treatment response) for African Americans delivering<37 weeks' gestation for rs471767 and rs578029, and for Hispanics/Caucasians delivering<37 weeks' gestation for rs500760 and <32 weeks' gestation for rs578029, rs503362, and rs666553.

CONCLUSION

The clinical efficacy and safety of 17-OHPC for recurrent PTB prevention may be altered by PGR gene polymorphisms.

Progesterone receptor genotype, family history, and spontaneous preterm birth

OBJECTIVE

To examine whether women with a personal or family history of preterm birth are more likely to have genetic variation in the human progesterone receptor (hPR).

METHODS

Women with a singleton preterm birth at less than 37 weeks of gestation between 2002 and 2006 were identified from a prospectively collected clinical and biologic obstetric database (cases). Women in the control group were those with only term deliveries at or above 38 weeks of gestation. The Utah Population Database was queried for family history (first- or second-degree relative) of preterm birth. DNA was extracted from stored buffy coats and genotyped for six single nucleotide polymorphisms in the hPR.

RESULTS

One hundred fifty-four patients (92 women in the preterm case group, 62 women in the term control group) were included. All were white or Hispanic. There were no statistical differences between white and Hispanic allele frequencies. Women in the preterm case group were more likely to carry the minor allele, G (minor allele frequency 0.29 compared with 0.18, P=.035) for rs471767, and were more likely to carry the GT haplotype across rs471767 and rs578029 compared with women in the term control group. Similar haplotype block variation was seen among women with preterm birth plus a family history of preterm birth.

CONCLUSION

Allele and haplotype frequencies in the hPR are significantly different among women with preterm birth and women with preterm birth plus a family history of preterm birth. This suggests the hPR gene may be a candidate for association with preterm birth or familial preterm birth.

LEVEL OF EVIDENCE

III.

Role of progesterone receptor polymorphisms in the recurrent spontaneous abortions: Indian case

Background

We attempt to ascertain if the 3 linked single nucleotide polymorphisms (SNPs) of the Progesterone Receptor (PR) gene (exon 1: G 1031 C; S344T, exon 4: G 1978 T; L660V and exon 5: C 2310 T; H770H) and the PROGINS insertion in the intron G, between exons 7 and 8, are associated with Recurrent Spontaneous Abortion (RSA) in the Indian population.

Methodology/Principal Findings

A total of 143 women with RSA and 150 controls were sequenced for all the 8 exons looking for the above 3 linked SNPs of the PR gene earlier implicated in the RSA, as well as for any new SNPs that may be possibly found in the Indian population. PROGINS insertion was screened by electrophoresis. We did not find any new mutations, not observed earlier, in our population. Further, we did not find significant role of the *2 allele (representing the mutant allele at the three SNP loci) or the T2 allele (PROGINS insertion) in the manifestation of RSA. We also did not find an LD pattern between each of the 3 SNPs and the PROGINS insertion.

Conclusions/Significance

The results suggest that the PR gene mutations may not play any exclusive role in the manifestation of RSA, and instead, given significantly higher frequency of the *2 allele among the normal women, we surmise if it does not really confer a protective role among the Indian populations, albeit further studies are required in the heterogeneous populations of this region before making any conclusive statement.

Preterm birth and inflammation-The role of genetic polymorphisms

Spontaneous preterm labour and preterm births are still the leading cause of perinatal morbidity and mortality in the developed world. Previous efforts to prevent preterm birth have been hampered by a poor understanding of the underlying pathophysiology, inadequate diagnostic tools and generally ineffective therapies. Clinical, epidemiological and experimental studies indicate that genito-urinary tract infections play a critical role in the pathogenesis of preterm birth. Moreover, intrauterine infection increases perinatal mortality and morbidity, such as cerebral palsy and chronic lung disease, significantly. It has recently been suggested that gene-environment interactions play a significant role in determining the risk of preterm birth. Polymorphisms of certain critical genes may be responsible for a harmful inflammatory response in those who possess them. Accordingly, polymorphisms that increase the magnitude or the duration of the inflammatory response were associated with an increased risk of preterm birth. In contrast polymorphisms that decrease the inflammatory response were associated with a lower risk of preterm birth. This article will review the current understanding of pathogenetic pathways in the aetiology of preterm birth.

Progesterone receptor gene polymorphisms are not associated with preterm birth in a Hispanic population

OBJECTIVE

To determine whether increased frequency of mutant alleles of the progesterone receptor gene (PGR) was associated with preterm birth in a population of Hispanic women.

METHODS

Placental DNA from 64 patients who had preterm births and 54 control patients was genotyped for 4 progesterone receptor gene polymorphisms by polymerase chain reaction (PCR) restriction fragment length polymorphism. The chi(2) test and t test were used to calculate statistical significance. Linkage disequilibrium was calculated using the Linkage Disequilibrium Analyzer program.

RESULTS

The genotypic frequencies of the 4 polymorphisms were not significantly different between the study and control groups. In addition, there was complete linkage disequilibrium between V660L, H770H, and PROGINS polymorphisms, but not with +331G/A polymorphism.

CONCLUSIONS

The present study suggests that polymorphisms in the progesterone receptor gene are unlikely to be associated with an increased risk of preterm birth in a Hispanic population.